240 A Short History of Astronomy [CH. ix. 



to grasp Newton's general ideas, even though the details 

 of his mathematics were out of their range. It was more- 

 over soon discovered that his scientific ideas could be 

 used with advantage as theological arguments- 



192. One unfortunate result of the great success of the 

 Prindpia was that Newton was changed from a quiet 

 Cambridge professor, with abundant leisure and a slender 

 income, into a public character, with a continually increas- 

 ing portion of his time devoted to public business of one 

 sort or another. 



Just before the publication of the Prindpia he had been 

 appointed one of the representatives of his University to 

 defend its rights against the encroachments of James II., 

 and two years later he sat as member for the University 

 in the Convention Parliament, though he retired after its 

 dissolution. 



Notwithstanding these and many other distractions, he 

 continued to work at the theory of gravitation, paying 

 particular attention to the lunar theory, a difficult subject 

 with his treatment of which he was never quite satisfied.* 

 He was fortunately able to obtain from time to time first- 

 rate observations of the moon (as well as of other bodies) 

 from the Astronomer Royal Flamsteed (chapter x., 197-8), 

 though Newton's continual requests and Flamsteed's occa- 

 sional refusals led to strained relations at intervals. It is 

 possible that about this time Newton contemplated writing 

 a new treatise, with more detailed treatment of various 

 points discussed in the Prindpia; and in 1691 there was 

 already some talk of a new edition of the Prindpia, possibly 

 to be edited by some younger mathematician. In any 

 case nothing serious in this direction was done for some 

 years, perhaps owing to a serious illness, apparently some 

 nervous disorder, which attacked Newton in 1692 and 

 lasted about two years. During this illness, as he himself 

 said, " he had not his usual consistency of mind," and it is 

 by no means certain that he ever recovered his full mental 

 activity and power. 



Soon after recovering from this illness he made some 



* He once told Halley in despair that the lunar theory ' made 

 his head ache and kept him awake so often that he would think ol 

 it no more." 



